Copper alloy for an electric connecting device

ABSTRACT

A copper alloy for an electric connecting device, having Cr in the range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %, and Sn in the range from 0.1 to 2.0 mass %, with the balance being inevitable impurities and Cu, wherein the copper alloy has tensile strength of 600 MPa or more, 0.2% yield strength of 560 MPa or more, electric conductivity of 40% IACS or more, and rupture time of 500 hours or more in a stress corrosion test under a load of 80% of the 0.2% yield strength.

TECHNICAL FIELD

The present invention relates to a copper alloy for a connecting deviceset up in electric wiring.

BACKGROUND ART

Electric connecting devices have been widely used for portions ofelectrical connection, such as electrical outlets of electric appliancesand switches of illumination. Metals are generally used for theconnecting portion, and electric contact is made by permitting themetals to contact to one another. There are two kinds of such electricconnecting portions: one is connection to an electric wire (copper wire)from which electricity is supplied, and the other is connection to anobject to which electricity is supplied. Pure copper, excellent inelectric conductance, and a copper alloy (such as C14410) in which atrace amount of Sn or Ag (≦0.2%) is added, to improve heat resistance,have been used in the contact portion.

The mechanical strength of these materials is so low. Therefore, tomaintain a contact to the aforementioned object to which electricity issupplied, the connecting portion employed a structure that the contactportion was reinforced using a high mechanical strength material, suchas stainless steel, as a spring material. However, since stainless steelis expensive, a high-mechanical strength copper alloy as a substitutefor stainless steel has been desired.

Since a technology to make a structure in which a “receiving blade(contact plate)”, which is an electronic contact portion, and a “springmaterial” are integrated, has been developed for reducing cost, ahigh-mechanical strength material that also functions as the springmaterial is being desired for the copper alloy.

In electric connecting devices, electric connection is achieved byallowing metals to contact one another. However, heat generation hasbeen a problem at the contact portion. It has been found thatmicro-electric discharge (glow) occurs at the contact portion,proliferation of cuprous oxide is induced by the micro-electricdischarge, to increase a contact resistance, thereby resulting in heatgeneration.

Accordingly, copper alloys for electric connecting device have beenproposed, by which glow and proliferation of cuprous oxide hardly occur,by reexamining alloy components (for example, JP-A-60-255944 (“JP-A”means unexamined published Japanese patent application)). However, themechanical strengths of such alloys are so poor that they were notsuitable as the spring material.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a copper alloyexcellent in mechanical strength, electric conductivity, stressrelaxation resistance, stress corrosion resistance, glow resistance,corrosion resistance, and the like.

Another object of the present invention is to provide a copper alloysuitable for electric connecting devices (electric wiring connectors),such as electrical outlets of electric appliances and switches ofillumination, that is able to prevent glow from occurring and cuprousoxide from being proliferated.

The inventors of the present invention have made detailed investigationson the contact portion of electric connecting devices, and havedeveloped a copper alloy excellent in mechanical strength, electricconductivity, stress relaxation resistance, stress corrosion resistance,and glow resistance.

The present invention provides:

(1) a copper alloy for an electric connecting device, comprising Cr inthe range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %,and Sn in the range from 0.1 to 2.0 mass %, with the balance beinginevitable impurities and Cu, wherein the copper alloy has tensilestrength (TS) of 600 MPa or more, 0.2% yield strength (YS) of 560 MPa ormore, electric conductivity (EC) of 40% IACS or more, and rupture timeof 500 hours or more in a stress corrosion test (SCC) under a load of80% of the 0.2% yield strength;

(2) the copper alloy for an electric connecting device as described in(1), which has stress relaxation property (SR) of 50% or less, in 1,000hours at 150° C.;

(3) the copper alloy for an electric connecting device as described in(1) or (2), comprising Si in the range from exceeding zero to 0.2 mass%; and

(4) the copper alloy for an electric connecting device as described in(1), (2), or (3), which is excellent in glow resistance.

Other and further objects, features and advantages of the invention willappear more fully from the following description, taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of stress corrosion resistance test(SCC), which was performed in the working example; and

FIG. 2 is a schematic view of an apparatus for measuring glow resistanceand cuprous oxide proliferation resistance, which apparatus was used inthe working example.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferable embodiments of the present invention will be described indetail.

The content of Cr is restricted in the range from 0.1 to 1 mass %. Thisis because, although Cr is an addition element which reinforces thealloy by causing precipitation in copper, Cr of less than 0.1 mass %hardly gives a sufficient precipitation hardening effect while Cr ofexceeding 1.0 mass % results in saturation of the effect and only causesunnecessary additional costs. The content of Cr is preferably 0.2 to 0.8mass %, more preferably 6.2 to 0.5 mass %.

The content of Zn and the content of Sn are restricted in the rangesfrom 0.1 to 5.0 mass % and from 0.1 to 2.0 mass %, respectively, becauseZn and Sn are elements that form solid solutions in copper and theyremarkably enhance mechanical strength and exhibit an effect forimproving stress relaxation resistance, in a solid-solution hardeningprocess and subsequent cold-working process. On the other hand, theseelements impair electric conductivity when too large amounts are added.These elements each exhibit insufficient effects when less than 0.1 mass% of these elements were added. When the amount of Zn exceeds 5.0 mass%, the alloy becomes poor not only in electric conductivity but also instress corrosion resistance and causes large proliferation amount ofcuprous oxide. When the amount of Sn exceeds 2.0 mass %, electricconductivity is affected. The content of Zn is preferably in the rangefrom 0.13 to 4.0 mass %, and the content of Sn is preferably in therange from 0.2 to 1.5 mass %.

Si contributes to prevention of hot-working-induced cracks. While aSn-containing alloy is known to have poor hot workability, addition ofSi reduces susceptibility to hot working. However, too large amount ofSi decreases electric conductivity. Therefore, the amount of Si ispreferably in the range from 0.001 to 0.1 mass %.

The copper alloy for an electric connecting device of the presentinvention can be produced by means of a general production methodinvolving appropriate repetition, for example, of rolling andheat-treating. Preferable production steps and conditions are asfollows, although the present invention is not restricted thereto:

(1) casting is preferably conducted by a continuous casting process;

(2) hot rolling is conducted at a temperature in the range from 900 to1050° C. (preferably 950 to 1030° C.) with a rolling ratio of 80% ormore (preferably 90% or more) followed by quenching;

(3) cold rolling is conducted with a rolling ratio in the range from 60to 98% (preferably 90 to 98%) under conventional conditions;

(4) heat treatment is conducted at a temperature in the range from 400to 500° C. (preferably 450 to 500° C.) for 1 to 5 hours; and

(5) finish working (cold rolling) is conducted with a reduction ratio of10 to 40%.

In the above, a heat treatment at a temperature in the range from 750 to900° C. (preferably 800 to 900° C.) for 0.1 to 1 minutes may beconducted between (3) and (4) or in the course of (4).

The copper alloy according to the present invention has tensile strengthof 600 MPa or more, preferably 600 to 700 MPa, and more preferably 600to 650 MPa.

The copper alloy according to the present invention has 0.2% yieldstrength of 560 MPa or more, preferably 580 to 680 MPa, and morepreferably 580 to 630 MPa.

The copper alloy according to the present invention has electricconductivity of 40% IACS or more, preferably 45 to 60% IACS, and morepreferably 50 to 60% IACS.

The copper alloy according to the present invention has rupture time of500 hours or more in a stress corrosion test, preferably 1000 hours ormore, and more preferably 3000 hours or more.

Mechanical strength (tensile strength and 0.2% yield strength) is aproperty in conflict with electric conductivity. In the case of thealloy system according to the present invention, an increase ofmechanical strength results in a reduction of electric conductivity,while an increase of electric conductivity results in a reduction ofmechanical strength. Further, mechanical strength is also in conflictwith bending workability. A higher mechanical strength is preferred, buta higher mechanical strength also results in a more deteriorated bendingworkability. In this connection, a higher electric conductivity allowsthe alloy to be applied to wiring devices that use high electriccurrent. Furthermore, reliability of the alloy increases as the timeuntil rupture becomes longer.

The present invention provides a copper alloy suitable for electricconnecting device excellent in mechanical strength, electricconductivity, and stress relaxation resistance, as well as in stresscorrosion resistance and glow resistance.

The present invention will be described in more detail based on thefollowing examples, but the present invention is not intended to belimited thereto.

EXAMPLES

Each copper alloy was cast into a book mold with a thickness of 30 mm, awidth of 120 mm, and a length of 180 mm, at a tapping temperature ofabout 1200° C., using an open-air high-frequency induction furnace, at amelting temperature in the range from about 1200 to 1250° C. Thethus-obtained ingot was kept at a temperature in the range from about950 to 1000° C. for 1 hour in an open-air heating furnace, and,subsequently, was finished into a plate with a thickness of about 12 to13 mm by hot rolling. The plate was further finished into a plate with athickness of about 10 mm by scalping the surface of the hot-rolledplate.

The plate was repeatedly subjected to cold working and heat treatment,to produce a flat plate (strip) with a thickness of 0.5 mm. The heattreatment for precipitating Cr was conducted at a temperature in therange from 400 to 450° C. for a time period in the range from 2 to 5hours, and the finish reduction ratio of 10 to 40%.

Commercially available plate materials with a thickness of 0.5 mm,comprised of copper alloys and non-iron materials, were purchased. Thecopper alloys were C2600, C2680, C5111, C5191, and C7701, and stainlesssteels were SUS301 and SUS304.

The tensile strength, 0.2% yield strength, electric conductivity, stressrelaxation property, stress corrosion property of each of thesematerials were investigated.

Regarding tensile strength (TS) and 0.2% yield strength (YS), a JIS-5test piece was cut out from each of these materials from a directionparallel to the roll direction, and the tensile strength and 0.2% yieldstrength were measured in accordance with JIS Z 2241.

Regarding electric conductivity (EC), a test piece with a width of 10 mmand a length of 150 mm was cut out from each of these materials from thedirection parallel to the roll direction, and electric conductivity wasmeasured in accordance with JIS H 3200, with an inter-terminal distanceof 100 mm.

The stress relaxation property (SR) was tested in accordance with theElectronic Materials Manufactures' Association of Japan Standards(EMAS-3003: a stress relaxation test method by bending of a springmaterial) using a cantilever method. The test sample was allowed tostand in a high temperature chamber (in open air) at 150° C. while thesample was loaded with 80% of the 0.2% yield strength obtained in thetensile strength test. This measurement was repeated in a prescribedtime interval up to 1000 hours.

The stress corrosion (SCC) test was conducted in accordance with anammonia test method in JIS C8306, wherein a stress was applied by themethod shown in FIG. 1. In the drawing, the reference numeral 10 denotesa test piece, the reference numeral 11 denotes a load, the referencenumeral 12 denotes a silicon cap, the reference numeral 13 denotes aglass cell, and the reference numeral 14 denotes an ammonia solution.The measurement was conducted as follows. A test piece 10 with a widthof 10 mm and a length of 100 mm was prepared, and, by applying a tape ormask, only an area of 10 mm (width)×10 mm (length) of the test piece wasexposed to a 3 vol. % ammonia (NH₃) atmosphere. The time from afterapplication of the load 11 until rupture of the test piece was measured.The loaded stress was 80% of the 0.2% yield strength obtained in thetensile strength test.

Glow resistance and cuprous oxide proliferation resistance were thenevaluated. FIG. 2 shows a schematic view of an apparatus used formeasuring glow resistance and cuprous oxide proliferation resistance.

Evaluation for glow resistance was performed as described below. Thatis, a copper wire 2 with a diameter 2 mm was attached to a holder 1equipped with a load applier, and a sample 3 of any one of the examplesaccording to the present invention or the comparative examples wasplaced on a sample holder 4. Then, the sample was brought into contactwith the copper wire 2, and a current flowing between the copper wire 2and the sample 3 was adjusted to 4 A, by means of Slidac 8 and avariable resistor 6. Then, the sample holder 4 was vibrated with avibrator 5, and the wave form of a voltage between the copper wire 2 andthe sample 3 was observed with an oscilloscope 7. When glow(micro-electric discharge) occurred between the copper wire 2 and thesample 3, it changed the wave form on the oscilloscope 7. A frequency(the number of times vibrated) applied until the occurrence of thechange in wave form was utilized to evaluate glow resistance. Withrespect to evaluation of glow resistance, though it may vary dependingon the application, when the number of vibration applied untiloccurrence of the change in wave form, which means occurrence of glow,is 1×10³ or less, it is judged to be “poor”; when said number is morethan 1×10³, it is judged to be “good”.

Evaluation for cuprous oxide proliferation resistance was performed asdescribed below. Vibration with the vibrator 5 was stoppedsimultaneously with the confirmation of the occurrence of glow, and thenthe sample 3 was left to stand for 60 minutes. Then, the sample 3 wastaken out, and then cuprous oxide formed on the surface of the sample 3was collected, to measure the mass thereof. The mass, i.e. theproliferated amount of cuprous oxide (mg), was utilized to evaluatecuprous oxide proliferation resistance. With respect to evaluation ofcuprous oxide proliferation resistance, though it may vary depending onthe application, when the mount of cuprous oxide formed (mg) is 200 mgor less, it is judged to be “good”, and when said amount is more than200 mg, it is judged to be “poor”.

The results of measurements are shown in Tables 1 to 4. In the tables,there are alloys showing plural values of mechanical strength, electricconductivity, and the like, even though they have the same components;these are test results obtained by changing the finish reduction ratiosof such alloys as shown in the tables.

TABLE 1 [Examples] Finish reduction Alloy Cr Sn Zn Si ratio TS YS EC SRSCC No (mass %) (mass %) (mass %) (mass %) (%) (MPa) (MPa) (% IACS) (%)(Hr) 1 0.15 0.5 0.8 — 35 635 604 53 36 >500 2 0.2 0.25 0.5 — 40 651 61957 41 >500 3 0.25 0.5 0.5 — 30 656 625 54 39 >500 4 — 40 708 687 5242 >500 5 0.25 0.5 2 — 30 765 756 51 45 >500 6 0.25 0.5 4 — 35 826 83150 48 >500 7 0.25 0.8 0.1 — 25 652 620 50 41 >500 8 — 40 704 682 4944 >500 9 0.25 0.8 0.25 — 20 653 621 50 38 >500 10 — 35 705 683 4941 >500 11 0.25 0.8 0.24  0.002 20 704 681 48 40 >500 12 0.25 0.8 0.250.01 20 709 688 44 39 >500 13 0.25 0.8 0.24 0.09 20 722 699 41 37 >50014 0.25 0.8 0.5 — 20 650 619 50 38 >500 15 — 30 702 681 49 41 >500 16 —40 723 719 48 44 >500 17 0.25 0.8 0.75 — 20 647 616 50 34 >500 18 — 30699 678 48 38 >500 19 0.25 0.8 1 — 20 653 621 49 29 >500 20 0.25 0.9 0.5— 20 653 621 49 34 >500 21 — 30 705 683 48 37 >500 22 0.25 0.9 0.7 — 30656 624 49 31 >500 23 0.25 1 0.1 — 30 649 618 48 35 >500 24 0.25 1 0.12 0.003 30 653 612 47 37 >500 25 0.25 1 0.15 0.02 30 655 633 44 35 >50026 0.25 1 0.12 0.09 30 667 623 41 33 >500 27 0.25 1 0.5 — 25 654 622 4840 >500 28 — 35 707 684 46 43 >500 29 — 40 728 723 45 46 >500 30 0.25 11 — 25 654 622 47 37 >500 31 0.25 1.2 0.25 — 25 645 614 45 34 >500 320.25 1.2 1 — 25 654 623 45 39 >500 33 0.25 1.5 0.25 — 25 647 616 4242 >500 34 0.3 0.2 0.5 — 30 655 623 57 41 >500 35 0.3 0.8 0.25 — 25 646614 50 38 >500 36 0.3 0.8 0.5 — 25 656 624 50 42 >500 37 — 35 708 686 4945 >500 38 0.3 0.8 1 — 25 649 618 49 40 >500 39 — 35 701 680 48 43 >50040 0.3 0.9 0.5 — 25 645 614 49 40 >500 41 — 35 697 675 48 43 >500 42 0.30.9 0.8 — 25 655 622 48 38 >500 43 0.5 1 0.5  0.003 25 646 614 4841 >500 44 0.5 1 1 0.01 35 653 622 47 37 >500 45 0.8 0.5 0.5 — 35 655622 54 39 >500 46 0.8 1 1 0.05 25 649 618 47 42 >500

TABLE 2 [Comparative examples] Finish reduction Alloy Cr Sn Zn Si ratioTS YS EC SR SCC No (mass %) (mass %) (mass %) (mass %) (%) (MPa) (MPa)(% IACS) (%) (Hr) 50 0.08 0.7 1 — 30 589 551 51 43 >500 51* 1.25 0.7 1 —35 653 621 51 32 >500 52 0.25 0.05 0.04 — 35 552 525 49 55 >500 53 35548 547 50 55 >500 54 0.25 0.09 0 — 40 550 524 65 54 >500 55 35 548 54663 55 >500 56 0.25 0 0.09 — 40 546 519 50 55 >500 57 50 547 541 5055 >500 58 0.25 1.6 0.2 0.02 30 651 620 32 33 >500 59 35 647 642 3837 >500 60 0.3 1.0 0.5 0.25 30 655 644 38 36 >500 61 0.3 1.2 0.5 0.5  30662 659 35 35 >500 62 0.25 0.5 5.5 — 25 651 619 53 35 480 63 — 30 648641 60 38 465 64 0.25 1.6 20 — 25 684 651 22 62 25 65 — 30 679 676 21 6522 Commercially available products 80 C1100 (Pure copper) H 320 304 9989 >500 material** 81 C2600 (Brass) EH 649 618 28 77 5 material** 82C2680 (Brass) EH 649 617 28 68 8 material 83 C5111 (Phosphor bronze) EH646 615 17 45 >500 material 84 C5191 (Phosphor bronze) EH 655 623 1245 >500 material 85 C7701 (Nickel silver) EH 656 624 8 8 >500 material86 SUS301 (Stainless steel) H 1211 1152 7 2 >500 material 87 SUS304(Stainless steel) H 1312 1247 6 3 >500 material *No. 51 is a referenceexample **In the above table, “H material” and “EH material” mean “Htempered material” and “EH tempered material”, respectively.

From the results shown in Tables 1 and 2, the followings are understood.

First, the comparative examples were evaluated as follows.

No. 50 was poor in mechanical strength, due to a small content of Cr.

No. 51 exhibited properties not different from those of the examples.However, addition of Cr in an excess amount results in saturation of itseffects and only results in an increased cost; thus not suited forpractical use.

Nos. 52 to 57, which contained Sn and Zn in small amounts, were poor inmechanical strength and were remarkably poor in stress relaxationresistance giving values exceeding 50%.

Nos. 58 and 59 were poor in electric conductivity.

Nos. 60 and 61 were poor in electric conductivity.

Nos. 62 to 65 were poor in stress corrosion resistance, due to a largecontent of Zn.

Among the commercially available alloys, No. 80 was poor in electricconductivity and further poor in evaluation items other than stresscorrosion cracking. The brasses of Nos. 81 and 82 were poor in electricconductivity and stress corrosion resistance. The phosphor bronzes ofNos. 83 and 84, the nickel silver of No. 85, and Nos. 86 and 87 werepoor in electric conductivity.

In contrast, examples Nos. 1 to 46 obtained the copper alloys forelectric connecting device excellent in all the properties, such astensile strength (TS), 0.2% yield strength (YS), electric conductivity(EC), stress corrosion resistance (SCC), and stress relaxationresistance (SR).

The results of the glow resistance test, and the amount of generatedcuprous oxide as a result of the test are shown in Tables 3 and 4.

TABLE 3 Amount Numbers until of occurrence of cuprous Alloy glowdischarge oxide No. (×10³ times) (mg) 1 18 19 2 25 40 3 20 45 4 14 68 526 86 6 21 94 7 15 14 8 23 31 9 16 56 10 21 93 11 21 53 12 21 15 13 14 314 25 38 15 21 93 16 18 55 17 25 86 18 20 56 19 18 10 20 25 45 21 23 10022 24 99 23 14 70 24 24 2 25 22 21 26 21 46 27 24 77 28 20 9 29 20 82 3020 64 31 17 35 32 25 118 33 23 108 34 25 95 35 16 41 36 13 26 37 21 3038 18 49 39 19 109 40 15 5 41 23 57 42 23 109 43 21 51 44 20 55 45 19 4946 24 98

TABLE 4 Amount Numbers until of occurrence of cuprous Alloy glowdischarge oxide No. (×10³ times) (mg) 50 11 40 51 19 33 52 17 49 53 2579 54 20 19 55 18 22 56 20 84 57 27 119 58 18 39 59 25 38 60 23 42 61 1922 62 16 35 63 24 90 64 14 46 65 17 86 80 17 9 81 19 451 82 29 428 83 23272 84 17 212 85 21 119 86 20 222 87 20 269

As is apparent from the results shown in Tables 3 and 4, the alloysaccording to the present invention had excellent glow properties.

Further, by considering the results shown in Tables 1 to 4synthetically, the alloys according to the present invention satisfiedrespective required properties, and thus were excellent as alloy forelectric connecting devices.

INDUSTRIAL APPLICABILITY

The copper alloy of the present invention has high mechanical strengthand high electrical conductivity and is excellent in stress relaxationresistance and corrosion resistance, and thus the alloy is suitable asthe copper alloy for electric connecting device.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.

1. A copper alloy for an electric connecting device, comprising Cr inthe range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %,and Sn in the range from 0.1 to 2.0 mass %, with the balance beinginevitable impurities and Cu, wherein the copper alloy has tensilestrength of 600 MPa or more, 0.2% yield strength of 560 MPa or more,electric conductivity of 40% IACS or more, and rupture time of 500 hoursor more in a stress corrosion test under a load of 80% of the 0.2% yieldstrength.
 2. The copper alloy for an electric connecting device asclaimed in claim 1, which has stress relaxation property of 50% or less,in 1,000 hours at 150° C.
 3. The copper alloy for an electric connectingdevice as claimed in claim 1, comprising Si in the range from exceedingzero to 0.2 mass %.
 4. The copper alloy for an electric connectingdevice as claimed in claim 2, which is excellent in glow resistance.